Various materials are used, particularly in construction, such as insulation foams, and adhesives, and grouts, which are dispensed from containers under pressure. Typically, the container will be pre-filled with the material, together with an inert gas, which is pressurized. The container has a manually operable valve. When the valve is open the pressure of the gas forces the material out of the container. As mentioned, such materials are widely used for insulation. Typically such insulation materials will be of the group known as polyurethane foam. However, other such materials are also packaged and dispensed from similar containers, for example joint filling compounds or grouts, adhesives and the like.
In the past, many of these materials have been packaged somewhat crudely in manually operable cartridges. The cartridge was simply a cylindrical sleeve of cardboard, with a nozzle at one end and a simple sheet metal piston at the other. Such cartridges could be placed in a manually operable dispensing device. The nozzle end was then cut off, and by means of a handle, a rod, and a lever the piston was forced along the cylindrical cartridge, thereby ejecting the material through the dispensing nozzle. However, these systems require very substantial manual effort in the lever. In addition the cartridges only contained a relatively small volume of material, and consequently they had to be replaced repeatedly. As a result, the packaging alone in such cartridges represents a substantial cost of the end product.
A further and more serious disadvantage is that the pressure with which the product is dispensed, depends essentially on the manual strength of the operator. Obviously a stronger man with a large hand can apply more pressure to the lever, than a man with less strength.
There is however a still further disadvantage. The force with which the material is ejected, on any given ejection stroke may vary, during the stroke, depending upon how steadily the manual pressure is applied and the mechanical advantage of the lever. In addition, the force applied to the stroke may vary from one stroke to another even by the same operator.
Consequently, there is a continual problem when using this type of manual dispensing cartridge, in that the "bead" of material being dispensed will vary in thickness and depth, from one stroke to another and even during the same stroke.
A further problem is that it is usually desired to apply a continuous "bead". However in the manual dispenser the lever had to be released and pressed repeatedly, causing intermittent pressure drops, with even the most skilled of operators.
Accordingly, in order to overcome a number of these problems, pressurized packages have been developed, in which the material to be dispensed is contained in a pressurized container which also contains a pressure medium such as an inert gas under pressure. Manually operable valves on such containers permit the material to be dispensed as desired. In such containers, since the pressure is dependent upon the pressure of the inert gas or medium, the ejection pressure is more or less constant so long as there is any material and gas left in the container.
However, the containers themselves have proved relatively inconvenient to use. The valve on such a container is usually a relatively small device at one end of the container. Consequently, in many cases it is not possible to apply the valve directly to the work piece, and some material becomes dispensed where it is not required and is wasted.
Accordingly, there have been developed by a number of companies a form of dispensing device or gun for use with such pressurized cartridges. Typically these guns will incorporate an elongated slender dispensing nozzle, and a cartridge mounting upon which the pressurized cartridge holding the material may be attached. Within the dispensing nozzle, a dispensing valve is provided. A manually operable trigger is provided on the dispensing gun. The trigger is connected to the valve, so that by operation of the trigger the valve can be opened thereby permitting the material to be dispensed through the nozzle onto the work piece. Such guns have achieved wide popularity since they enable a workman to dispense the material directly into the precise location required on the work piece with little or no wastage.
The pressure is both constant, independent of the operator strength, and continuous, so long as the trigger is pressed. The majority of such dispensers or guns on the market all have the same basic design features. However, in all of them, the actual construction of the dispensing gun requires the manufacture and assembly of a large number of parts, all of which must be made to careful tolerances, and which must be assembled by skilled workmen. Internal seals are provided where necessary to prevent the material under pressure from entering portions of the gun where it is not required.
Usually, the manufacturers of the materials, or the manufacturer of the gun, or both will supply a solvent type of cleaner which is forced through the gun at the end of the days work, to clean it.
Unless this cleansing operation is performed immediately after use, the material will cure within the body of the gun, and the gun will then be rendered useless. This in fact is what occurs, not infrequently. Bearing in mind the high cost of these dispenser guns, it will be appreciated that this can cause problems for a small contractor. Another disadvantage of these relatively complex sophisticated dispensing guns is that their high cost tends to limit the actual sales of the material itself. There may be many handymen, and do-it-yourself householders, who would wish to use such pressurised materials for sealing cracks, or for grouting, or closing spaces around window and door openings, so as to improve the insulation and weather proof characteristics of a home. However, the cost of the dispensing gun itself represents a relatively substantial investment to such persons. Accordingly, unless they are prepared to make this investment, it may well be that they will simply not buy the pressurised material at all. It will thus be appreciated that to some considerable extent the sales of such materials are limited to professional insulation and construction firms. The small handyman and the home owner market have remained virtually closed to this type of material. Clearly, it would be desirable to provide a low cost dispensing gun for use with these pressurized materials. If a dispenser could be produced at a low enough cost that it could be virtually used for one day and then discarded, it would enable a home handyman or home owner to buy a few containers of the material, and a dispenser and do a day's work, an then simply throw away the empty containers, and also the dispenser itself.
For the sake of economy, the dispenser should preferably be of such a design that it consists of only two or three separate parts. However, it is also desirable that it can easily be taken apart and washed out with solvent, so that it can be reused several times before it is discarded, if desired.